This is one OTL-1 power supply.
It weighed 100 pounds and could regulate 350 volts at 10 amps from Hz
to 200 KHZ at full power plus/minus 3%. In effect it is a 5,000 watt
solid state amplifier, and each audio channel of the OTL-1 used one
of these. This was the first time in the audio arts that anyone ever
actively regulated that power supply of an OTL amplifier which is a
daunting challenge because this type of circuit, unlike a transformer
coupled amplifier, is both high voltage and high current.

Why am I showing you this? When
tube amplifier designers say that active regulation doesnt work,
or they cant do it...nonsense!